As is well understood in the art, demand for hydrocarbon fluids continues to steadily increase while supplies and reserves continue to decline. Consequently, many lower-yield reserves are being exploited. Many of those lower-yield reserves produce hydrocarbons at low pressure, especially coal-seam methane wells, shallow oil and gas wells, and the like. Such low pressure wells are commonly produced using low-pressure wellhead equipment such as screwed independent wellhead equipment, well-known in the art. Nonetheless, the completion and/or re-completion of such wells generally requires high pressure stimulation treatments to ensure viable production. Such high pressure stimulation treatments are often performed at high pump rates and high fluid pressures. Although well tree isolation tools are commonly used to isolate wellhead equipment from direct exposure to those fluid pressures. Nonetheless, the well tree isolation tool is mounted to the well tree, and the lifting pressure on the tool resulting from the high pump rates and elevated fluid pressure of the well stimulation fluids can, and has on occasion, over stressed the holding strength of the threaded connection between the casing and the wellhead or a tensile strength of one of the wellhead components. If that connection gives way, workers in the vicinity can be fatally injured by ejected equipment and control of the well is lost, resulting in the escape of hydrocarbons to the atmosphere.
This problem is not exclusive to screwed independent wellheads, however. As is well understood in the art, pump rates and fluid pressures used to stimulate wells equipped with medium pressure flanged wellheads sometimes exceed the tensile strength of the flanged wellhead components. If a tensile strength of a flanged wellhead component is exceeded, rupture can occur resulting in the ejection of equipment from the well, with all of its attendant hazards.
While many different well tree isolation tool configurations and many different pack-off assemblies for those tools are known, there is no known tool that is configured to reduce lift pressure on wellhead components during a well stimulation treatment. Pack-off assemblies for well tree isolation tools seal off against the well casing or tubing to isolate wellhead components from high fluids pressures. Nonetheless, that seal does nothing to control the lift pressure exerted on the wellhead components to which the wellhead isolation tool is mounted.
Consequently, there exists a need for a wellhead isolation tool that not only seals off against the casing but also locks the well tree isolation tool to the casing to transfer lift pressures directly to the casing and thereby ensure that high pressure stimulation can be safely conducted at pressures that exceed the holding and/or tensile strength of wellhead components.